Incandescent lamps having a press-sealed base are well known in the art. Examples of such lamps are disclosed in U.S. Pat. Nos. 4,243,907, 4,603,278 and 4,749,901. U.S. Pat. No. 4,243,907 discloses a lamp having a sealed envelope with a press-seal at one end. The press-seal has removable portions to reduce the width of the press-seal.
U.S. Pat. No. 4,603,278 discloses an electric lamp having a sealed, light-transmitting glass envelope comprising a bulbous portion and a press-sealed end portion. One or more filaments are located within the interior of the bulbous portion. Lead-in conductors are connected to the filament or filaments. Each conductor is sealed within the press-sealed end portion of the envelope and projects exteriorly of the envelope. The lamp includes an electrically insulating base member having an opening for receiving the press-sealed end portion of the envelope and a protruding section for being positioned within an electrical socket. The base member includes flexure means for enabling the opening that receives the press-sealed end portion to expand during the insertion of the press-sealed end portion of the envelope into the base member.
U.S. Pat. No. 4,749,901 discloses a lamp and a method of preparing the same. The lamp has a bulbous portion and a flattened base. The method of manufacturing the lamp includes the steps of evacuating the lamp through a hollow space formed in the flattened base, press-sealing the flattened base of the lamp with press jaws whose pressing surface is substantially flat and flowing a cooling gas through the hollow space while maintaining the patency of the hollow space. The patent discloses an improvement wherein relief grooves on the surface of the press jaws are eliminated. The lamp includes at least one filament and corresponding electrical connections. The electrical connections are press-sealed in the flattened base. Furthermore, the lamp includes a support collar for positioning the incandescent lamp in a socket.
In the past, incandescent lamps were manufactured by providing a glass envelope having an open end; inserting a mount assembly comprising a filament or filaments and corresponding lead-in conductors or wires to the interior of the envelope with sections of the conductors extending to the exterior of the lamp; inserting a glass or other tube into the interior of the envelope through the open end; press-sealing a portion of the envelope around the tube and the conductors; evacuating the interior of the envelope through the tube following the press-sealing step, flowing an inert gas or gases into the interior of the envelope following the evacuating step; and closing the inlet of the tube to prevent the flow of the inert gas out of the lamp or the flow of undesirable gases into the lamp through said tube.
The manufacturing process for making miniature incandescent lamps suitable for use in automobiles by Wagner Lighting Products, a Division of Cooper Industries, Inc., is now described to illustrate a method of making an incandescent lamp which has been used heretofore. Referring to FIG. 1, there is shown a pre-formed glass envelope 10 having a bulbous portion 12 and a tubular portion 14 extending from bulbous portion 12. A mount assembly 15 including filaments 16 and 18 is inserted into the interior of envelope 10. Lead-in conductors 20 and 22 are connected to the ends of filament 16 and lead-in conductors 24 and 26 are connected to the ends of filament 18. Lead-in conductors 20, 22, 24 and 26 pass through bridge 28 which maintains the lead-in conductors in a spaced-apart relationship to one another. The end portions of lead-in conductors 20, 22, 24 and 26 which are not connected to filaments 16 and 18 extend to the exterior of envelope 10 through tubular portion 14. Mount assembly 15 which is comprised of filaments 16 and 18, lead-in conductors 20, 22, 24 and 26, and bridge 28 is preassembled prior to its insertion into envelope 10.
A glass exhaust tube 30 having a tube inlet 32 and tube outlet 34 is axially inserted into tubular portion 14. Heat is applied to tubular portion 14 to make it suitable for press-sealing. After heating and while a cooling gas is flowing through exhaust tube 30, the bottom section of tubular portion 14 is compressed by press jaws (not shown) to form a press-sealed base (shown in FIG. 2) around exhaust tube 30 and lead-in conductors 20, 22, 24 and 26. The press-sealed base so formed extends from the bottom end of envelope 10 which was previously defined by the open end of tubular portion 14 to immediately adjacent the mouth of tube outlet 34 without sealing tube outlet 34.
Referring now to FIG. 2, there is shown glass envelope 10 having bulbous portion 12 and tubular portion 14 whose lower section has been pressed as previously described to form a press seal 40. Press seal 40 encloses lead-in conductors 20, 22, 24 and 26 and exhaust tube 30 which now provides fluid communication between the interior of envelope 10 and the exterior thereof. Lead-in conductors 20, 22, 24 and 26 are retained in a spaced-apart configuration by bridge 28. Tube outlet 34 is unobstructed to provide fluid communication between tube 32 and the interior of envelope 10.
Following the press-sealing step described above, inlet 32 of exhaust tube 30 is connected to a vacuum pump (not shown) and the gaseous contents of envelope 10 are removed by applying a vacuum thereto. Inlet 32 of exhaust tube 30 is then removed from the vacuum pump and is exposed to a source of inert gas. The pressure difference between the pressure of the source of the inert gas and the pressure of the interior of envelope 10 which is under vacuum causes the inert gas to flow into the interior of envelope 10. After envelope 10 is filled with inert gas, heat is applied to exhaust tube 30 immediately adjacent press-sealed base 40 to remove the portion of exhaust tube 30 that extends exteriorly of press-sealed base 36 and to close exhaust tube 30 thereby obstructing the fluid communication between the interior and exterior of envelope 10 through exhaust tube 30 and sealing the inert gas in the interior of envelope 10.
One disadvantage of the prior methods including the prior method described above is that they utilize a two-step process to replace undesirable gases in the envelope with inert gases, namely, evacuating the undesirable gases by a vacuum pump and exposing the evacuated envelope to a source of inert gases. Another disadvantage is that the sealing provided by the press-sealed base around the exhaust tube is not leak proof, and with the passage of time, inert gas escaped from the interior of the envelope through an escape passage existing between the exhaust tube and the press-sealed base.
The above disadvantages are overcome by the present invention which provides a one-step process for displacing the undesirable gases from the glass envelope and replacing them with inert gases, eliminates the problem of gas leakage between the exhaust tube and the press-sealed base, and provides a positive injection of inert gas to the interior of the glass envelope whereby the amount of inert gas trapped within the envelope is higher than the amount achieved by the prior art processes.
These and other advantages of the present invention will become apparent from the following description.